International Journal of Emerging Technology and Advanced Engineering Website: www.ijetae.com (ISSN 2250-2459, Volume 2, Issue 1, February 2012)

Simulation and design of low cost single phase solar inverter Nishit Kapadia1, Amit Patel2, Dinesh Kapadia3 1

2

M.Tech student, Electrical engineering department, Institute of Technology, Nirma university, Ahmedabad Assistant professor, Electrical engineering department, Institue of Technology,Nirma university, Ahmedabad 3 Manager, R&D Department, Hitachi Hi-Rel Powerelectronics Pvt. Ltd., Gandhinagar 1

[email protected] [email protected] 3 [email protected] 2

This electrical energy is in DC form. This dc voltage is boosted using dc to dc boost converter. This boosted dc voltage is fed to inverter. Inverter converts dc voltage into ac voltage. Here sine coded PWM push-pull inverter is used. The output of inverter is given to step-up transformer and low-pass filter which will give 220V 50Hz sine wave output. This output is given to the load.

Abstract— How solar energy is converted into electrical energy in cost effective manner. The main components of this solar system are solar cell, dc to dc boost converters, inverter. Sine wave push pull inverter topology is used for inverter. In this topology only two MOSFETs are used and isolation requirement between control circuit and power circuit is also less which helps to decrease the cost of solar inverter. In this paper design of components for booster and inverter are done. Simulation of solar inverter is done and simulation results for different conditions are taken. Keywords—Low cost solar inverter, Solar inverter, Single phase solar inverter.

Inverter topology is sine wave push pull inverter is selected. This topology is used to decrease the cost of solar inverter. In this topology only two MOSFETs are used. And the isolation requirement between control and power circuit is less.

I. INTRODUCTION

II. BLOCK DIAGRAM

There are two types of sources for electrical power generation. One is conventional and other is nonconventional. Today to generate most of electrical power conventional sources like coal, gas, nuclear power generators are used. Some of conventional source are polluted the environment to generate the electricity. And nuclear energy is not much preferable because of its harmful radiation effect on the mankind. After some of ten years conventional sources will not sufficient enough to fulfill the requirements of the mankind. So some of the electrical power should be generated by non-conventional energy sources like solar, wind .With the continuously reducing the cost of PV power generation and the further intensification of energy crisis, PV power generation technology obtains more and more application.

Block diagram of single phase solar inverter is shown in Fig 1.1. Solar panel output is 24volt. Dc to dc boost converter converts 24 volt dc voltage to 36 volt dc. This dc voltage is converted to ac voltage using inverter. Inverter output is sine coded PWM pulses. This sine coded pulses are stepped up using step up transformer. These sine coded PWM pulses are converted into sine wave using lowpass filter. This sine wave ac voltage is fed to the load. The ac output is 220volt 50Hz. For design the output power of solar inverter is taken 250VA. III. DESIGN OF DC TO DC BOOST CONVERTER AND INVERTER Inverter is designed for output power of 250 VA. Power factor is taken 0.8. Therefore output power of inverter is 200 watt. Overall inverter efficiency of inverter is taken 97%. From this output power of booster is taken 206.18 watt. Overall booster efficiency is taken 97.5%. From this input power of booster is 211.47 watt.

In this paper cost effective method is used to implement single phase solar inverter. Solar cell/ PV cells convert solar energy into electrical energy.

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International Journal of Emerging Technology and Advanced Engineering Website: www.ijetae.com (ISSN 2250-2459, Volume 2, Issue 1, February 2012)

230V AC 50Hz

36 V DC

LOAD Solar Panel Transformer

24V DC

DC to DC Boost

Inverter

Figure 1.1 Block diagram of single phase solar inverter

Converter

Minimum input voltage to the booster is 21V. Maximum input voltage of the booster is 27V. Output voltage of booster is 36V. Relation between input voltage and output voltage is given by equation 3.1. Vo =

From this formula inductance L is calculated 1357.67 µH. Maximum input current of booster with 150% overloading is 16.61A. So inductor for booster should be designed for value L = 1357.67 µH and current I = 16.61A. Ripple voltage is taken as 1%Filter of output voltage which is 0.36V.Output current of booster is calculated from output power and output voltage which is 5.7274A.Capacitance of booster is given by equation 3.3. From equation 3.3 value of capacitance C for dc to dc boost converter is 1357.67 µH.

x Vin ………………………..(3.1) where Vo = output voltage, Vin = input voltage, δ = duty cycle

Duty cycle δ for minimum and maximum input voltage is 0.4167 and 0.25 respectively. Switching frequency of MOSFET is taken 3.2 kHz. Switching period is 312.5 us. From this on time of MOSFET for minimum and maximum input voltage are 130.2 µs and 78.125 µs respectively. From minimum input voltage and input power input current is calculated 10.07A. Current ripple ∆Iin is taken 20% of input current. So current ripple ∆Iin is 2.014A. In steady state condition in on state of MOSFET the voltage equation of booster is given by equation 3.2. Vin = L x

Low-pass filter

C=

…………………….(3.3)

where Io = Output current of MOSFET, ∆Vo = Output voltage ripple Booster component values inductance L = 1357.67 µH and Capacitance C = 2071.53 µH are found. Booster output voltage Vob = 36V Modulation index for inverter m = 0.97 Inverter transformer regulation r = 5%

……………………..(3.2)

Transformer primary voltage Vp = Vob * = √ 23.419 V Transformer efficiency ηt = 0.97 Safety factor SF = 1.1 Inverter MOSFET current or Transformer primary current

where L = inductance, ∆I = current ripple, Ton = On time of MOSFET

Ip =

159

√

= 25.679A

International Journal of Emerging Technology and Advanced Engineering Website: www.ijetae.com (ISSN 2250-2459, Volume 2, Issue 1, February 2012) MOSFETs of inverter have this current rating.

Output of PI controller = (Kp * e) +

IV. SCHEMATIC AND CONTROL STRATEGIES OF DC TO DC BOOST CONVERTER AND INVERTER

Where Kp = Proportional gain, e = error and Ti = Integration time

∫

……… (4.1)

Schematic and close loop control for dc to dc boost converter is shown in the figure4.1(a). As the solar panel voltage varies according to weather so to make the output of dc to dc boost converter constant close loop control is required. In the figure for close loop control PI (Proportional and Integral) controller is used.

Figure 4.2(a)

Figure 4.1(a)

Figure 4.2(b) Fig 4.2 (a) Schematic of booster and inverter (b) Sine PWM generation using sine triangular comparison

Output of dc to dc boost converter is given to inverter. The schematic which contains inverter and booster is shown in Fig 4.2 (a) and Fig 4.2 (b) shows the generation of PWM pulses for inverter. To generate PWM pulses simple sine triangular comparison is used. As shown in Fig 4.2(a) sine wave push pull inverter topology is used. Main Advantages of this topology are: (I) Only two switches/MOSFETs are used (ii) Isolation requirement between control and power circuit is less. These advantages help to decrease the cost. A step up transformer is used in the output of inverter to step up the ac voltage. A low pass filter is used to get the sine wave at the output.

Figure 4.1(b) Figure 4.1(a) Close loop schematic of booster (b)Close loop control system for booster

To control the output voltage of booster PI controller is used which is shown in Fig 4.1(b). As shown in Fig 1.2 (b) reference voltage is compared with actual output voltage and error in output voltage e is calculated. Error e is passed through PI controller. The output of PI controller is given by equation (4.1). The output of PI controller is compared with triangular wave which will generate pulses which is given to the MOSFET of the dc to dc boost converter. So close loop control makes the output voltage of dc to dc boost converter constant.

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International Journal of Emerging Technology and Advanced Engineering Website: www.ijetae.com (ISSN 2250-2459, Volume 2, Issue 1, February 2012) V. SIMULATION AND SIMULATION RESULTS Simulation is carried out in PSIM software. Simulation results for dc to dc boost converter are shown in Fig 5.1. Fig 5.1(a) and (b) shows the results for input voltage 21V and output voltage 36V at no load and full load respectively. Fig 5.1(c) shows the result for input voltage transition from 27V to 21V. And it is shown in the figure though the input voltage changes from 27 V to 21V output voltage remains constant at 36V. PI controller is used to make output voltage constant at 36 V volt level. Fig 5.1(d) shows the simulation result for step load applied and step load removed .It is shown in the figure though step load is applied or removed the output voltage is remains constant at 36 V voltage level. PI controller is used to make output voltage constant at 36V volt level.

Figure 5.1(c)

Figure 5.1(d) FIG.5.1 (A) Booster output at no load (B) Booster output at full load (C) Booster output for input voltage transition from 37 volt to 21 volt (D)Booster output for step load applied and removed

Figure5.1(a)

In FIG.5.2 (A) sine triangle comparison and generation of sine PWM is shown. Here 50Hz sine wave is compared with 3.2 kHz triangular wave which will generate sine PWM. In figure 5.2 (B) inverter output without low pass filter is shown. In FIG.5.2 (C) the inverter output for full load condition for simulation time 1.3 s to 1.5 s. FIG.5.2 (C) shows that RMS value of output voltage and current of inverter are 220.09 V and 0.905 A. In FIG.5.2 (D) the inverter output for no load condition for simulation time 1.3s to 1.5s. FIG.5.2 (D) shows that RMS value of output voltage and current of inverter are 220 V and 11 mA .

Figure 5.1(b)

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International Journal of Emerging Technology and Advanced Engineering Website: www.ijetae.com (ISSN 2250-2459, Volume 2, Issue 1, February 2012)

Figure 5.2(d) FIG.5.2 (a) Sine Triangle comparison and PWM generation (b) Inverter output without low pass filter (c) Inverter output for full load condition (d) Inverter output for no load condition

Figure 5.2(a)

VI. CONCLUSION Use of sine wave push pull inverter reduces the cost of single phase solar inverter considerably. In this topology only two switches are used and the isolation requirement between control and power is less. Advantages of this topology help to decrease the cost. Value of the components for dc to dc boost converter and inverter is calculated. This calculated value of components is used to simulate dc to dc boost converter and inverter. Simulation for different conditions viz. no load, full load, load transition and input voltage transitions are carried out and found satisfactory.

Figure5.2(b)

References [1] Fernando Lessa Tofoli, Julio Cesar Sconell, Carlos Alberto Gallo, Sergio Manuel Rivera Sanhuenza, A LOW COST SINGLE-PHASE GRID-CONNECTED PHOTOVOLTAIC SYSTEM WITH REDUCED COMPLEXITY, IEEE 978-1-4244-3370-4/09,2009. [2] Yishu Zhao, Yan Zhang, Depeng Wang, Jie Zhan, THE CIRCUIT TOPOLOGY FOR SINGLE-PHASE GRID CONNECTED SYSTEM AND THE CONTROL TECHNOLOGY ON CONVERTERS, IEEE TRANSECTIONS ON ELECTRONIC DEVICES,VOL 48,NO.5,2001. [3] D.Barater, G. Franceschini, E.Lorenzani, UNIPOLAR PWM FOR TRANSFORMER LESS GRID-CONNECTED CONVERTERS IN PHOTOVOLTAIC PLANTS, IEEE 978-1-4244-2544-0/08, 2009 [4] Muhammad H. Rashid, “Power electronic Circuits, Devices and Application Handbook”, Third Edition, Chapter 3, page no 108-111, Page no 250-253 [5] Paul C. Krause, Oleg Wasynczuk, Scott D. Sudhoff, “Analysis of Electrical Machinery And Drive Systems, Wiley Student Edition, second edition,Chapter 1, page no1-8

Figure 5.2(c)

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International Journal of Emerging Technology and Advanced Engineering Website: www.ijetae.com (ISSN 2250-2459, Volume 2, Issue 1, February 2012) [6] M D Singh, K B Khanchandani, “POWER ELECTRONICS”, TATA McGRAW HILL company, Second edition,Chapter9, page no 540570 [7] Soeren Baekhoej Kjaer, John K. Pedersen,Frede Blaabjerg, A Review of Single-Phase Grid-Connected Inverters for Photovoltaic Modules, IEEE TRANSECTIONS ON INDUSTRY APPLICATION VOL. 41 NO.5 SEPTEMBER/OCTOBER2005 [8] Pedro Gomes Barbosa, Henrique Antonio CarvalhoBarga, Marcio do Carmo Bardosa Rodrigues, Estevao Coelho Teixeria, Boost Current Multilevel Inverter and Its Application on Single-Phase GridConnected Photovoltaic Systems, IEEE TRANSACTIONS ON POWER ELECTRONICS VOL.21 NO.4 JULY 2006 [9] Yilmaz Sozer and David A. Torrey, Modeling and Control of Utility Interactive Inverters, IEEE TRANSACTIONS ON POWER ELECTRONICS VOL.24 NO.11, NOVEMBER 2009 [10] Freddy Chan and Hugo Calleja, Reliability Estimation of Three Single-Phase Topologies in Grid-Connected PV Systems, IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS VOL 58. NO.7 JULY 2011 [11] Roberto Gonzalez, Jesus Lopez, Pablo Sanchis and Luis Marroyo, Transformerless Inverter for Single-Phase Photovoltaic Systems, IEEE TRANSACTONS ON POWER ELECTRONICS, VOL.22 NO.2, MARCH 2007 [12] Michale E. Ropp and Sigifredo Gonzalez, Development of a MATLAB/Simulink Model of a Single-Phase Grid-Connected Photovoltaic System, IEEE TRANSACTIONS ON ENERGY CONVERSION

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